1. Field of the Invention
The present invention relates to a guillotine-type cutting machine and more particularly to an improvement in a cutter blade for cutting a large number of stacked large size sheets or plates.
2. Description of the Related Art
Cutting machines are used to cut a stack, which includes a large number of thin sheets or plates such as paper sheets, plastic sheets, aluminum plates, etc., into a plurality of predetermined small size sheets. The cutting machines are of a guillotine type in which a single-edged cutter blade is moved vertically to cut the sheets. The cutter blade has a cutting face and a vertically flat face or a back face intersecting the cutting face to form a cutting edge. In cutting the sheets, the cutting face pushes cut sheets away from the stack while the flat face is made to face the cut surface of the stack.
Such a cutter blade tends to have cutting dust stuck thereto after only a few cutting operations, depending on the material of the sheets and the number of sheets in the stack. The dust causes scratches to be formed on the cut surface of the sheets. Conventionally, various countermeasures have been taken to prevent this problem. For example, in the case of cutting a stack of aluminum sheets, a paper laminated with a polyethylene is interposed as a interleaf between each of the aluminum sheets, or a lubricant is applied to the cutter blade as described in Japanese Patent Laid-Open Publication No. 2-109699.
However, when cutting a stack of metallic sheets with paper interposed, the cutting edge of the cutter blade is damaged after as few as 10 cuts, which causes the cut surface of the metallic sheets to be scratched linearly by cutting dust. Also, the dust adheres to the back face of the cutter blade because of heat generated in cutting to cause a built-up edge portion to be formed on the cutting edge.
It is known to form cutter blades with a flank in their back faces in order to prevent formation of a built-up edge portion. However, conventionally, the inclinations of the flanks with respect to the moving direction of the cutter blades are approximately only 0.02.degree.. Accordingly, a built-up edge portion still is formed quickly. Therefore, it is necessary to change the cutter as often as every 10 cuts, resulting in degradation of efficiency of the cutting operation.